This study of patients with osteoporosis comprises a systematic outpatient and or inpatient assessment of a careful history for risk factors, state of bone (bone density in spine, proximal femur and radius), skeletal activity (serum osteocalcin, alkaline phosphatase, urinary hydroxyproline, iliac bone biopsy), and secondary causes of bone loss (e.g. thyroid function, adrenal status). The ultimate goal is to develop a "metabolic classification" of osteoporosis.